Calibration of four degree of freedom Robotworld modules

Many industrial applications are well suited to nonanthropomorphic pick and place robots. Robotworld is adept at performing vertical assembly operations, which may constitute 60% of all manufacturing operations. Furthermore, nonanthropomorphic robots can achieve higher accuracy than anthropomorphic (six degree of freedom) robots because they can be calibrated to higher precision. In this report we describe calibration techniques for Robotworld modules, simple four degree of freedom (x, y, z, θ) manipulators. Robotworld modules consist of base which is actuated in (x, y) via Sawyer motors, and a servo-controlled rotating and translating end effector arm, which extends downward from the base. Robotworld modules are implicitly coordinated in x and y (to 0.025 mm) because all the Sawyer motors are actuated with respect to the same platen; therefore, only the axes of rotation and translation of the end effector arm, need to be calibrated. We estimated these axes by localizing a calibration peg using multiple crossbeam sensors. We analyzed the performance of our calibration technique via self validation methods and found that as few as 40 observations provided reasonably high precision (0.025 mm root mean squared error)